"the imprisoning of Merlin, maybe, by the damsel Nimue"

 Merlin and Nimue are characters from Arthurian legend. Merlin is the great sorcerer who advises King Arthur, and Nimue (also known as Vivien, and a host of variations on both names) is the Lady of the Lake, who gives King Arthur his sword, Excalibur. Merlin is in love with Nimue, but she eventually enchants and imprisons him (in a cave, or under a mountain or rock).